Foundry binder systems which cure with gaseous sulfur dioxide are known in the art. U.S. Pat. No. 3,879,339 for instance discloses that certain synthetic resins can be cured in the presence of an oxidizing agent and sulfur dioxide. Examples of such resins are furan, urea formaldehyde, and phenol formaldehyde resins.
On the other hand, U.S. Pat. No. 4,526,219 discloses that certain ethylenically unsaturated materials can be cured by a free radical mechanism in the presence of an oxidizing agent and sulfur dioxide. Additionally, U.S. Pat. No. 4,518,723 discloses that blends of epoxy resins and certain ethylenically unsaturated materials can be cured in the presence of an oxidizing agent and gaseous sulfur dioxide.
It is clear from U.S. Pat. Nos. 4,525,219 and 4,518,723 that the systems disclosed therein, preferably incorporate significant amounts of ethylenically unsaturated monomers, generally trimethylolpropane triacrylate, as a reactive diluent, in order to obtain the desired physical properties for the foundry shapes made with these binder systems.
All of the systems described have the advantages of extended benchlife and foundry shapes can be made with the binder systems with excellent physical properties.
A problem with the systems which utilize trimethylolpropane triacrylate as the reactive diluent is that they are expensive. Therefore, it would be desirable to eliminate or at least minimize the use of such ethylenically unsaturated monomers. This has not been possible in the past without significantly sacrificing the physical properties of the foundry shapes made with the binder systems.